Week 1 - Part 2

Question 1

Why can’t we, from our position inside the Milky Way Galaxy, see through to its far rim (at least not with ordinary light)

Answer 1

because the space between the stars is not completely empty.

Question 2

The space between the stars contains a sparse distribution of ………. (mostly the simplest element, ………..) intermixed with tiny solid particles that we call ………. ………..

Answer 2

gas / hydrogen / interstellar dust.

Question 3

From various investigations, we have evidence that much of our Galaxy is made of material we cannot currently observe directly with our instruments. We therefore call this component of the Galaxy ……….. …………

We know the ……….. ……….. is there by the pull its gravity exerts on the stars and raw material we can observe,

Answer 3

dark matter

Question 4

In a number of places, enough stars have formed together that we recognized them as ……….. ……….

Answer 4

star clusters

Question 5

(We define the universe to be everything that exists that is accessible to our …………….)

Answer 5

observations

Question 6

When they were first discovered, some astronomers called galaxies ……….. ……….

Answer 6

island universes

Question 7

(A ………….., we should note, is one of the ………… sections into which astronomers divide the sky, each named after a prominent star pattern within it.)

Answer 7

constellation / 88

Question 8

The nearest galaxy, discovered in …………., is a small one that lies ………….. light-years from the Sun in the direction of the constellation …………., where the smog in our own Galaxy makes it especially difficult to discern.

Answer 8

1993 / 70,000 / Sagittarius

Question 9

Beyond this Sagittarius dwarf galaxy lie two other small galaxies, about 160,000 light-years away. First recorded by Magellan’s crew as he sailed around the world, these are called the ………… …………

All three of these small galaxies are satellites of the Milky Way Galaxy, interacting with it through the force of gravity. Ultimately, all three may even be swallowed by our much larger Galaxy, as other small galaxies have been over the course of cosmic time.

Answer 9

Magellanic Clouds

Question 10

The nearest large galaxy is a spiral quite similar to our own, located in the constellation of ……………., and is thus called the ……………… galaxy; it is also known by one of its catalog numbers, …………..

Answer 10

Andromeda / Andromeda / M31

Question 11

M31 is a little more than 2 million light-years away and, along with the Milky Way, is part of a small cluster of more than 50 galaxies referred to as the ………. ………..

Answer 11

Local Group

Question 12

Some of the clusters themselves form into larger groups called …………….

The Local Group is part of a …………. of galaxies, called the …………… …………….

Answer 12

superclusters / supercluster / Virgo Supercluster

Question 13

At even greater distances, where many ordinary galaxies are too dim to see, we find ………….

These are brilliant centers of galaxies, glowing with the light of an extraordinarily energetic process.

Answer 13

quasars

Question 14

the four elements most common in life on Earth— …………………………..

Answer 14

hydrogen, carbon, nitrogen, and oxygen.

Question 15

All atoms consist of a central, positively charged ………… surrounded by negatively charged ……………

Answer 15

nucleus / electrons

Question 16

The bulk of the matter in each atom is found in the nucleus, which consists of positive …………. and electrically neutral …………… all bound tightly together in a very small space.

Each element is defined by the number of …………… in its atoms.

Answer 16

protons / neutrons / protons

Thus, any atom with 6 protons in its nucleus is called carbon, any with 50 protons is called* *tin, and any with 70 protons is called ytterbium**.

Question 17

Remarkably, physicists have discovered that everything that happens in the universe, from the smallest atomic nucleus to the largest superclusters of galaxies, can be explained through the action of only four forces: ……………., ……………. (which combines the actions of electricity and magnetism), and two forces that act at the nuclear level.

The fact that there are four forces (and not a million, or just one) has puzzled physicists and astronomers for many years and has led to a quest for a unified picture of nature.

Answer 17

gravity, electromagnetism

Question 18

Name them

Answer 18

Question 19

The widest diameter of the ellipse is called its ……….. ………… Half this distance—that is, the distance from the center of the ellipse to one end—is the ……….. ………., which is usually used to specify the size of the ellipse.

For example, the ………… ……….. axis of the orbit of Mars, which is also the planet’s average distance from the Sun, is 228 million kilometers.

Answer 19

major axis

semimajor axis / semimajor

Question 20

Explanation of Eccentricity

Answer 20

https://www.youtube.com/watch?v=I5VMppoi_EY

Question 21

Using Brahe’s data, Kepler found that Mars has an elliptical orbit, with the Sun at one focus (the other focus is …………..). The eccentricity of the orbit of Mars is only about 0.1; its orbit, drawn to scale, would be practically indistinguishable from a circle, but the difference turned out to be critical for understanding planetary motions.

Answer 21

empty

Question 22

Two points in any orbit in our solar system have been given special names. The place where the planet is closest to the Sun (helios in Greek) and moves the fastest is called the ………… of its orbit, and the place where it is farthest away and moves the most slowly is the …………..

For the Moon or a satellite orbiting Earth (gee in Greek), the corresponding terms are ……….. and ………….

Answer 22

perihelion / aphelion

perigee / apogee

Question 23

The main difference between asteroids and comets is their composition, as in, what they are made of. Asteroids are made up of metals and rocky material, while comets are made up of ice, dust and rocky material. Both asteroids and comets were formed early in the history of the solar system about 4.5 billion years ago. Asteroids formed much closer to the Sun, where it was too warm for ices to remain solid. Comets formed farther from the Sun where ices would not melt. Comets which approach the Sun lose material with each orbit because some of their ice melts and vaporizes to form a tail.

Answer 23

R 2

Question 24

The Moon is said to be ………….. when it is in the same general direction in the sky as the Sun (position A). Here, its illuminated (bright) side is turned away from us and its dark side is turned toward us.

In this phase the Moon is invisible to us; its dark, rocky surface does not give off any light of its own.

Because the new moon is in the same part of the sky as the Sun, it rises at sunrise and sets at sunset.

Answer 24

new

Question 25

But the Moon does not remain in this phase long because it moves eastward each day in its monthly path around us. Since it takes about 30 days to orbit Earth and there are 360° in a circle, the Moon will move about 12° in the sky each day (or about 24 times its own diameter). A day or two after the new phase, the thin crescent first appears, as we begin to see a small part of the Moon’s illuminated hemisphere. It has moved into a position where it now reflects a little sunlight toward us along one side. The bright crescent increases in size on successive days as the Moon moves farther and farther around the sky away from the direction of the Sun (position B). Because the Moon is moving eastward away from the Sun, it rises later and later each day

Answer 25

R 2